1. Field of the Invention
The invention relates to an electrostatic discharge protection structure, and more particularly, to an electrostatic discharge protection structure capable of preventing the latch-up issue caused by unexpected noise.
2. Description of the Prior Art
Electrostatic discharge (ESD) is an effect of electric charges moving rapidly between two electrically charged objects through a discharge path in a short period of time caused by contacting or short circuiting. Electrostatic discharge can damage components of an integrated circuit. Since the human body, machines used to package integrated circuits, and instruments for testing integrated circuits are all common charged bodies, the static electric charges of a charged body may discharge to a chip and cause irreversible harm to the chip once the charged body contacts with the chip. Therefore, an electrostatic discharge protection device is designed to provide a discharge path and to protect the integrated circuit from being blown out by an instantaneous discharge current.
In addition to the electrostatic clamp, which is a known electrostatic discharge protection apparatus, silicon controlled rectifier (SCR) is another popular electrostatic discharge protection apparatus. When an SCR is triggered by a triggering voltage, it will go into a snapback breakdown condition. Once the SCR enters the snapback breakdown condition, the SCR will become a low resistance path and clamp the holding voltage in a lower level. The low resistance path can provide a discharge path when the electrostatic discharge occurs so the discharge current will not flow through the integrated circuit and damage the chip.
However, the holding voltage is found to be much smaller than the power supply voltage for high-voltage devices. Such characteristics will cause the IC to be susceptible to the latch-up danger in practical system applications.